Why is Earth so special? Why did life develop and thrive here and (as far as we know) nowhere else in the Solar System? These are questions scientists and science fiction writers alike must puzzle over. Part of the answer may involve Earth’s ginormous moon.

Although Luna is not the largest moon in the Solar System (that honor goes to Ganymede), the mass ratio between Earth and Luna is way, way out of whack compared to other planet/moon combinations. A moon as large as Luna has no business orbiting a planet as small as Earth.

So what’s the effect of Luna’s relatively large size?

Scientists have speculated that Luna’s gravity does more than create tides. It may also help stabilize Earth’s orbital axis.

According to at least some computer simulations, Earth could easily tilt sideways by as much as 85 degrees if not for Luna’s constant gravitational tug. This would lead to sudden and dramatic changes to the global climate. Changes that life might not be able to cope with.

If that’s true, then disproportionately large moons like Luna may be necessary for all life-bearing planets. Since Luna-like moons are surely rare, this drastically limits the chances of finding life elsewhere in the universe. Which totally sucks (not a scientific evaluation, just my opinion).

However, there may be other possibilities. For example, some simulations indicate that a moonless Earth could still keep itself balanced thanks to the gravitational influence of Jupiter.

The lesson for science fiction writers is that life-bearing planets probably need something to hold them steady. Whether that something is a Luna-like moon, a Jupiter-like planet, or some other large nearby object is up to the writer’s imagination. At least until science provides us with more conclusive data.

You may think science fiction writers don’t need to know much about Earth. Sci-Fi is (stereotypically) about exploring space, visiting alien planets, and leaving the homeworld’s cradle behind. So I almost skipped Earth for my Solar System series.

Then I realized that learning how Earth formed, how life evolved here, and why life continues to thrive on this one planet could help me understand what alien worlds might look like.

Studying Earth has left me with a lot to think about. Since this is my final post for Earth month, I thought I’d review some of my still germinating thoughts about life and the environments that might support it.

Life tends to develop only in chemically active environments. Earth shows plenty of chemical activity, most notably oxygen-based chemistry. As a comparison, the surface of Mercury has virtually no chemical activity, and therefore it’s unlikely life in any form could develop there.

More energetic chemical reactions allow for more complex organisms to evolve. Chemical reactions involving oxygen can provide far more energy than a single-celled organism needs, which allows for multi-cellular life forms to develop. Other chemical reactions, like those involving sulfur on Venus, might not provide enough excess energy for anything larger than a microbe.

Microbial life may be absurdly common in the universe, taking advantage of every chemically active niche it can find. Microbes of some kind could exist on Mars or even Venus. They could live on certain moons of Jupiter and Saturn. They might even be able to eek out an existence among asteroids and comets.

Complex life, on the other hand, may be exceedingly rare. It’s hard to find a chemical that is as profitable, from an energy production standpoint, as oxygen. I’m sure there are viable alternatives, but the list would be short, and this would limit opportunities for the evolution of multi-cellular organisms even in a universe teeming with microbes.

Of course, this is all speculation. Speculation that comes after months of exhausting, headache-inducing research—but still just speculation.

Until scientists can confirm the existence of life on Mars, Venus, or elsewhere, and until they collect more data on the environmental conditions of Earth-like planets orbiting other stars, this is the most realistic picture of life in the universe that I can invent.

So what do you think? Am I on the right track, or is there something I’ve overlooked? Any suggestions on other avenues of research I should pursue? Please leave your thoughts in the comments below. I look forward to getting other people’s perspectives on these questions.

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Today’s post is part of Earth month for the 2015 Mission to the Solar System. Click here for more about this series.

The biggest problem with rockets is that they have to carry their own fuel. How much fuel they need to, for example, lift off from Earth is modeled using the ideal rocket equation. Thanks in part to a pesky logarithm embedded in that equation, rockets departing from Earth need to be 80-95% fuel by mass. And thus, spaceflight is absurdly expensive.

It’s not surprising, then, that engineers all across the globe have tried to think up an alternative means to reach space. What is surprising is that many of these engineers, often working independently of each other, have all come up with basically the same wacky idea: space elevators.

How to build a space elevator

First off, don’t picture a traditional elevator. Many early proposals for space elevators were essentially really tall towers with really long elevator shafts up the middle. At this point, it’s pretty clear that won’t work.

Instead, the current scheme is to launch a spacecraft into orbit carrying a spool of sturdy but lightweight material, something like a ribbon of carbon nanotubes. Once in orbit, the ribbon would be unspooled and slowly lowered back to the ground.

After the unspooling process is complete, the ribbon would be held taught on one end by Earth’s gravity and on the other by a counterweight, which would exert an enormous amount of centrifugal force due to Earth’s rotation.

An orbital station would be positioned near the ribbon’s center of mass. Ideally, that point should be located approximately 36,000 kilometers above Earth’s surface (for perspective, Earth’s diameter is roughly 12,000 kilometers). This is the altitude required to maintain geostationary orbit.

How to use a space elevator

In a proof of concept test during the 2009 X-Prize competition, a miniature space elevator car climbed a 900-meter cable dangling from a helicopter. And it did it in less than eight minutes. All we have to do now is scale up!

Unfortunately, real space elevators will probably be much slower, mainly for safety reasons. According to an article from New Scientist, it looks like a trip all the way up a full-sized space elevator would take roughly two or three weeks. So bring something to read. You’ll also need snacks.

However, your elevator car will not need to carry its own fuel, meaning it is no longer constrained by the rocket equation! The most popular design at the moment involves high-powered lasers which transmit electricity to the car as it goes. So fuel would constitute almost 0% of the total mass, rather than 80-95%.

Crazy enough to work?

So why haven’t we done this yet? We have the technology. Well, all but one component: the carbon nanotube ribbon. We can barely make carbon nanotubes longer than a few centimeters, so a 36,000+ kilometer ribbon is out of the question—for now.

Real life space elevators are decades or maybe centuries away. In the meantime, the construction, maintenance, and defense of these futuristic Towers of Babble could be fertile ground for new science fiction stories.

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Today’s post is part of Earth month for the 2015 Mission to the Solar System. Click here for more about this series.

What a fun coincidence that Earth day happens to fall in the middle of Earth month here on Planet Pailly! I thought we’d take a moment to see how some of the other planets in the Solar System have helped us better understand and appreciate the planet we call home.

NASA’s original mission statement included the words “to understand and protect the home planet.” One of the best ways to learn about Earth is to compare and contrast it with its neighbors. We’re just beginning to locate Earth-like planets orbiting other stars, which will no doubt teach us even more.

And that is one of the big reasons why it’s worth celebrating planetary science on Earth Day.

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Every Friday, we take a look at a new and interesting scientific term to help us all expand our scientific vocabularies together. Today’s word is:

IDEAL ROCKET EQUATION

April is Earth month here on Planet Pailly, but after two weeks of blogging about the planet Earth, I’m ready to move on.

Unfortunately, escaping Earth’s gravity is far easier said than done. The high, high cost of getting to space can be quantified using something called the ideal rocket equation (also known as Tsiolkovsky’s rocket equation or simply the rocket equation).

The equation is as follows:

∆v = ve ln(m0/m1)

Delta-v (∆v) represents the total change in velocity you’re aiming to achieve in any rocket-propelled maneuver, including liftoff. In order to reach low Earth orbit from the ground, your delta-v must equal at least 9.4 kilometers per second. To get that value, you’ll need to adjust the other variables in the equation.

Initial mass (m0): The total mass of your spacecraft plus the mass of your fuel and fuel tanks.

Final mass (m1): The total mass of your rocket after the maneuver is complete.

Effective exhaust velocity (ve): This is basically how much thrust your rocket can produce.

Increasing your rocket’s initial mass (by adding more fuel) will help increase your delta-v. Decreasing your final mass (by not only using up fuel but also shedding empty fuel tanks as you go) will also increase your delta-v. In fact, the greater the difference between the initial and final mass, the greater your delta-v will be, according to this equation.

However, increasing the difference between initial and final mass only creates a logarithmic increase in delta-v (the “ln” part of the equation is a natural logarithm). This means that adding more and more fuel produces diminishing returns. At some point, this is no longer a cost effective way to increase your delta-v.

Your other option is to use a more energetic fuel, increasing your effective exhaust (ve). Unfortunately, modern rockets already use some of the most effective chemical fuels available. With current technologies, the only way to significantly improve the ve part of the equation is with nuclear powered rockets, which might raise a few safety concerns, to say the least.

What Does All That Mean?

Due to the rocket equation, fuel constitutes 80 to 95% of a rocket’s mass at launch. Even a tiny satellite requires absurd amounts of fuel to reach space. This means launching anything into space is expensive (sometimes prohibitively expensive).

The problems associated with the ideal rocket equation are usually glossed over or ignored in science fiction by invoking new technologies or new laws of physics. But embracing the rocket equation and world-building within its limitations could lead to an intriguing setting for a Sci-Fi story. More on that in next week’s edition of Sciency Words.

P.S.: It’s possible that somewhere in the universe, life has evolved on a planet with even higher surface gravity than Earth’s. If so, these aliens would have an even harder time reaching space than we do. In fact, for some alien civilization out there somewhere, the rocket equation may make it effectively impossible to leave their home planet at all.

In a recent post, I suggested a story setting: a future where Earth, ravaged by a runaway greenhouse effect, has transformed into a clone of Venus. Today, I’d like to suggest an alternative: a future where Earth’s climate stabilized, more or less, thanks to the efforts of resourceful human beings.

Of these two possible futures, I think the latter is more believable. I say that partly because I’m an optimist when it comes to human nature, and given recent developments, I think my optimism may be justified.

The ozone layer is recovering: in the 1980’s, chlorofluorocarbons (or C.F.C.s) were banned due to their effect on the ozone layer. Now, decades later, the ozone layer is showing the first hints of recovery. Click here for more information.

We can have solar power at night: solar power isn’t perfect. Among its many problems is the rather obvious fact that it doesn’t work at night. But new facilities like the Solana Generating Station in Arizona can store excess heat collected from sunlight, and that heat energy can continue generating power for up to six hours after sunset. Click here for more information.

Global Carbon Emissions Flatline: carbon emissions tend to drop only when the economy slumps, but in 2014, for the first time since we started tracking these things, the economy grew without the usual increase in carbon emissions. If this trend continues, maybe we can save the planet and have plenty of money in our bank accounts. Click here for more information.

The situation is far from ideal. Some of the chemicals that replaced C.F.C.s harm the environment in other ways. Solana still struggles with energy production during the winter. Projections still show the planet will warm slightly, even though we’ve curtailed our carbon emissions somewhat.

But we’re making progress. As a global community, we’re making smarter decisions about energy production. I think one of the reasons climate change is such an uncomfortable topic is that most of the time, the situation seems hopeless, but we now have a few good reasons to be optimistic.

Believing a problem can be solved is the first step toward solving it. With climate change, the problem is starting to look solvable. So maybe Earth in the distant, Sci-Fi future won’t look like another Venus after all.

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Today’s post is part of Earth month for the 2015 Mission to the Solar System. Click here for more about this series.

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Every Friday, we take a look at a new and interesting scientific term to help us all expand our scientific vocabularies together. Today’s word is:

OXYGEN CATASTROPHE

If an extraterrestrial intelligence were to examine Earth from a distance, perhaps analyzing the spectral lines of Earth’s atmosphere, Earth might not seem like the most hospitable of planets. The atmosphere contains one of the most dangerous substances in the known universe: oxygen.

Earth Before Oxygen

In the beginning, Earth had an atmosphere composed mainly of carbon dioxide. Life thrived in this environment until someone (I’m looking at you, cyanobacteria) discovered the secret to photosynthesis: the ability to draw energy from sunlight.

Unfortunately, photosynthesis produces oxygen as a byproduct. As the cyanobacteria population boomed, so too did the oxygen content of both the oceans and the atmosphere. This led to Earth’s first mass extinction event: the oxygen catastrophe.

That’s Too Much Oxygen!

Oxygen is a highly reactive gas. It’s so reactive that one of the most common types of chemical reactions—oxidation—is named after it. Oxygen will do just about anything to react with other substances, and it doesn’t care who gets hurt in the process.

Here are some of the ways oxygen harmed Earth’s earliest organisms:

Oxygen oxidized minerals in the oceans, robbing microbial life forms of vital nutrients, causing many microbes to starve to death.

Oxygen sucks at trapping heat, so as atmospheric oxygen levels climbed, global temperatures plummeted. In fact, Earth may have briefly looked a little like the planet Hoth from Star Wars. End result: many microbes froze to death.

And that was the end of life on Earth, or at least it should have been.

Breath Easier Thanks to Aerobic Respiration

Aerobic respiration is a biological process that puts oxygen’s oxidizing tendencies to good use. Through aerobic respiration, glucose molecules (a.k.a. sugar) are disassembled, releasing enormous quantities of energy stored within glucose’s chemical bonds—far more energy than we could get without oxygen’s help.

During the height of the oxygen catastrophe, a handful of clever microbes figured out this aerobic respiration thing. They also developed special enzymes to protect themselves from the ravages of prolonged oxygen exposure. Atmospheric oxygen levels dropped to safer levels, the planet thawed, and a new balance was achieved between respirating and photosynthesizing organisms.

In fact, aerobic respiration has been so successful that it’s hard for us to think of oxygen as a deadly poison. Rather, it’s become a source of life. As for the cyanobacteria that started this whole mess, they’re still here, unrepentant, continuing to spew their oxygen waste all over the place.

So if an extraterrestrial intelligence were to examine Earth from a distance and notice the high oxygen content of the atmosphere, this might not be an obvious sign of life. But oxygen atmospheres don’t just happen. Something has to make them happen, and something has to maintain them over time. That should be enough to at least leave our E.T. friends scratching their heads.